Spinal cord injury (SCI) results in permanent functional deficits due to disruption of axonal connections. Attempts to repair injured spinal cord have been focused on axon regeneration in order to re-establish connections between the brain and the spinal cord below the injury level. Contusive injury, which is the most frequent type of injury occurring in human patients, leads to a formation of cystic cavities at the lesion epicenter. The cavity formation is one of major obstacles for axonal regeneration since injured axons fail to reach caudal tissue in the absence of physical and mechanical supports from extracellular matrix (ECM). Implanting artificial scaffolds has been proposed as a promising approach, but successful bridging with scaffolding biomaterials has not been convincingly demonstrated in clinically relevant contusive SCI model. Unpredictable and irregular geometry of lesion cavities formed in this model would necessitate the use of injectable hydrogel for this purpose. In the present study, I injected temperature sensitive poly(phosphazene) hydrogel, with a sol-gel transition behavior at 37°C, into the lesion epicenter in contusive rat SCI model at 1 week after injury. The hydrogel injection almost completely prevented cavity formation. In animals with the hydrogel injection, the lesion epicenter was replaced by fibronectin (FN)-enriched ECM by 4 weeks after the injection. The FN-positive ECM was surrounded by GFAP positive glial scars with an interface laden with chondroitin sulfate proteoglycans. Injection of hydrogel mixed with Taxol, which was previously reported to selectively suppress fibrotic scars, resulted in the failure of bridging cavities, suggesting a role of ECM produced by fibroblasts in the hydrogel effects. Interestingly, zymography showed upregulation of MMP-9 activity in animals with the hydrogel injection, and MMP-9 was highly expressed at the center of the FN-enriched ECM. The cellular source for the MMP-9 immunoreactivity was CD11b positive macrophages. Co-localization of FN and collagen-1α1 suggested that the majority of the newly formed ECM originates from perivascular fibroblasts.Animals with hydrogel injection showed improvement in coordinated locomotion as evidenced by BBB test and Catwalk analysis. The improvement in locomotor function was accompanied by better preservation of myelinated white matter around the lesion epicenter. Our study establishes a proof of principle that the temperature-sensitive hydrogel can be used as a cavity-bridging therapy for contusive SCI. Considering the versatility of hydrogel in a sol state incorporating various drugs and cells, this approach can also be utilized as a platform for multifaceted combinatorial therapy.